Learn about oil tank decommissioning

oil tank Certification

Getting a certification for the decommissioning of an underground storage tank requires doing a few things. Mostly in order to make sure the tank doesn’t pose a health risk now or in the future.

HOTs or any UST that is being decommissioned have to meet a few requirements in order to be considered valid by the DEQ and to get an official decommissioning letter.

The tank must be empty and clean, so that nothing else can leak out of it later. If the tank has clean soil samples then decommissioning in-place can happen.

The soil around the tank must have had little or no environmental impact. Oregon and Washington have different rules regarding the exact amount leakage that requires mitigation via soil removal. This step requires soil samples taken at specific locations and depths. Then there is a transfer of the soil samples and a legal chain-of-custody form to an analytical laboratory.

The clean and empty tank must be backfilled with a space-filling and inert material. This is so there is no sinkhole or depression when the steel tank eventually rusts away.

After reaching these requirements the tank becomes eligible for certification. Once proof of the work and soil sample results are ready the DEQ can review the report for approval.

The state of Oregon actually allows homeowners to do their own decommissioning. If you are planning to buy a home where the homeowner did the work we suggest taking another set of soil samples to verify the work. If you would like to see the heating oil tank service providers with a state license, click here.

How to Decommission an Oil Tank

You may wonder how to decommission an oil tank. The process of oil tank decommissioning depends on the site conditions. Let’s have a look.

The most common situation:

Where there is only one oil tank found in the oil tank search, the tank is in the yard, and the tank top is less than 5′ below the ground surface, and the soil samples are not too high. – This is a straightforward oil tank decommission.

Tank decommissioning process

At least 2 workers will be present by law. They will dig a hole directly over the center of the tank is possible. A 2′ X 3′ hole is big enough for most tanks. If the tank is deep the hole will need to be bigger to allow the shovel to work properly.

Once they reach the tank they will cut off the top to allow access into the tank. The technicians will then empty the tank of all liquid inside which almost always includes a layer of watery sludge. They can then clean the tank and will probably use either a vacuum truck and pressure washer or bucket and scraping tool.

The next step is to collect soil samples and inspect the tank. Workers put on Tyvek suits and respirators and after they establish a safe atmosphere inside the tank they ensure adequate airflow and enter it. If previous soil samples shows no contamination then there is no need for new samples unless they see holes inside the tank. If the workers see holes inside then they collect samples from under the area with holes.

The day of decommissioning after the cleaning the workers cover and fence-off the hole that accesses the tank; to secure the hole from pets and children. They place the samples on ice until they go to the lab for overnight testing via a private courier. The soil sample results take one business day to get back.

If the tank has not leaked workers will come back and backfill the tank with an approved material. Usually perlite, gravel, or concrete.

If the tests show hydrocarbon contamination then the DEQ will want more information before issuing a certification. Assessing the extent of the contamination is the next step.

When the soil samples are high:

With a non-detect result the tank needs no more sampling. This is a result below 50 ppm (parts per million). 50 ppm is also nearly the resolution limit of diesel oil detection.

If some contamination is present but it can be shown to not be a large spill then the tank can stay in place. If contamination is high the DEQ will want to remove the tank and the affected soil under it. When it is too dangerous to remove soil then a provider can do further testing to see if a health risk is present. They can add a vapor reduction system if contaminated air is present but removal of contaminated soil is not possible.

When soil samples show oil contamination over at 10,000 parts per million (PPM) then the DEQ wants further tests. If this soil volume is over 65 cubic yards then the soil needs to be removed or additional testing needs to be performed to prove there are no health risks. This can include sub-slab vapor sampling and water samples taken from multiple locations.

In Washington if the PPM is over 2,000 tank removal is the way to certification.

A ‘Risk Based Analysis’ is made on a contaminated site. This is a method of ‘boxing off’ the dirty soil with clean soil and finding out the maximum physical volume of contaminated soil. This involved multiple soil sampling bores in the yard and possibly in the neighbor’s yard.

When there is Poor access to the tank

There can be tanks inside homes if there are additions. Tanks can be underground beneath decks, driveways, walkways, garages, pavers and gardens.

For an additional fee workers will remove & replace deck boards and cut & replace holes in concrete or asphalt.

When there is no access to the tank

How to decommission an oil tank if you can’t get to it?

If the tank is more than 5′ down OSHA will not allow hand digging to the tank without shoring and shoring cannot fit in a hole that small.

A sinkhole or tank collapse may threaten the structural integrity of a home if the house is on top of a tank.

In situations where access is impossible, a tank service provider may perform a triple rinse. When they can only obtain one soil sample they can use mathematical modeling to figure out a ‘rate of reduction’.

With enough time, and tests, and money, almost any tank can get a DEQ certification of oil tank decommissioning.

When decommissioning is over

After filling the tank the packed soil should be left in a mount, this will enable it to settle. If the soil if put back without a mound there will be a depression later after it rains a few times.

Basic oil tank decommission cost?

If a tank search shows only one tank during a $100 tank search, and there is no contamination, the cost to decommission the tank will be around $1,000.

When soil samples show oil contamination the next step is a risk based analysis which adds around $2,000.

If significant leakage is present then the cost to mitigate it can be high. Removal of a tank can add an additional $3,000.

Other things can quickly increase the cost of tank decommissioning such as impacted groundwater or a large volume of contamination.

In some cases the total cost can exceed $10,000 for remediation.

When buying a home (which is already expensive) we highly recommend getting a $100 oil tank search. You or your clients may save you thousands of dollars in the future.

How much Time to decommission an oil tank?

A minimum of a few days. Each subset requires it’s own timeframe. The company performing the work has to wait until their workers have an opening on the schedule. They have to wait for 811 to come out to perform utility locates. There is the time to have the samples tested at the lab. Finally there is the time to schedule the filling of the tank (or other next steps).

Most decom’s happen as part of a real estate deal. Where the buyer makes an offer that the seller accepts and they get 10 days to perform their inspections.

Once a tank search is scheduled 811 can be called to do a utility locate so gas or water lines aren’t hit during potential soil sampling. This is at least a 2 day lead time.

After the search and locate of a tank a call to 811 will help workers to locate any underground utilities. No one wants a flood or gas leak in their new home. Then day that the workers take the soil sample they will transfer it to a lab for overnight testing. Finally, communication of results to the client is by phone the next business day.

If there is no contamination the workers can come back out and backfill the tank usually within a few days.

So, how long does it tank to decommission a UST?

Assuming there is no backlog of work and there is no soil contamination then a decommission can happen in less than a week.

See the most common sizes of residential heating oil tanks on our chart

a chart of fuel levels of oil tanks of different sizes

Underground Heating Oil Tanks, and many Underground Storage Tanks (HOTs & USTs) are almost always a set size.

Aboveground Storage Tanks also come in set sizes.

Most underground tanks are 44″ or 45″ in diameter, you still can find 52, 42, 40, and 36 inch diameter residential tanks.
The most common length for residential oil tanks around Portland is by far the 8′ long tank. While the 8’X45″ tank is called a ‘675 gallon’ tank is actually only 630 or 660 gallons in most cases. The 4′ long tank is the second most common and is more likely in smaller homes or in Vancouver.

Above ground tanks, as seen in a basement, garage, crawlspace, or on the side of the home, are usually 275 or 330 gallons. These tanks are often 5′ or 6′ long, 27-29″ wide, and 44-55″ tall. Any tank 10% or more buried counts as a UST. Because of this ASTs usually come with riser legs or blocks.

Are there different ways to decommission a heating oil tank? For Oregon homes, Yes!Both ‘in place’ and ‘by removal’ options exist.

In-place vs decom by removal

Previous to around 2007 most tank decoms were via removal. Removal of the tank was common. When soil samples showed oil contamination then the soil under the tank would be removed. To replace the volume of soil taken away use of sand, clean fill dirt, crushed concrete, or gravel was common. The Oregon DEQ assessed the data they had collected and issued new guidelines governing the amount of contamination allowed to stay in the ground.

This means less removals, which means less tractor marks and unsightly holes in yards. And easier for everyone if the tank is under Grandma’s prize rose bushes. Or uphill, in the backyard, or inaccessible corner of the property.

If a tank has leaked the Oregon DEQ will allow up to 65 cubic yards of contaminated soil at up to 10,000 PPM (1% by weight). This is a large volume of soil, but the presence of groundwater or high contamination can swiftly meet it.  Once exceeded the DEQ will require soil removal and possibly air sampling to give a certification.

If there is no access to the tank or a danger from accessing it you can pay extra to have a ‘triple rinse’. This is much less effective than a traditional decommission at cleaning the tank but meets the DEQ’s requirements. Pumping the tank full of a concrete sully is the last step.

For homes in Washington there is a strict limit, and any contamination over this limit requires removal of the tank and contaminated soil.

What’s a tank decommission?

Oil Tank Decommissioning is the process of taking a out of service while assessing and remedying any impacted soil. The tank decommission process may involve a search for groundwater if contamination is present.

An ‘Out-Of-Service’ is when workers empty and clean a tank but don’t tank soil samples.

Heating Oil Tanks (HOTs) aren’t they only thing you can decommission. Any Underground Storage Tank (UST) can be a hazard. Either due to collapse /sink hole or to contamination of the soil . Things such as gasoline tanks or bio-diesel tanks can also get a decommissioning.

Perform a decommission to find out if there are any health hazards from the tank and to asses them and mitigate them if present.

Get answers to your questions about Heating Oil Tank Decommissioning by clicking the + next to your question. More information below. Also view the info page and the FAQ on oil tank locating, and the ultimate Homebuyer Inspection Package our tank, sewer, radon combo sale.

See Photos related to decommissioning

Oil tank basic information: The oil tank sweep cost is $125.  An oil tank decommission cost is at least $1,000 and is usually closer to $3,000 to remedy. The worst cases can cost over $30,000 to remediate. For a house worth a quarter million dollars or more the cost for an oil tank search seems well worth it. The seller is usually the one to pay for the extent of the work. However the buyer usually covers the cost of soil testing for an underground tank starts which is around $200.

It’s normally much more cost effective for the buyer to schedule an Oil Tank Search then it is to be the seller and have to pay for the oil tank decommissioning in the future. To find a company that can help you decommission a heating oil tank check out the Oregon DEQ’s list of approved Heating Oil Tank service providers in the Portland, Oregon area. Read that list here or download a copy of that list by clicking here.

Read about the different certification types from the DEQ by clicking here, or read the heating oil tank FAQ from the DEQ by clicking here.

See, fuel levels in tanks of various sizes

a chart of fuel levels of oil tanks of different sizesAnd common sizes of oil tanks

tank size chart

Don’t see your question? Jack has years of experience working with heating oil tanks. You might even call him an oil tank specialist. Tank Decommissioning used to be his full time job, doing 2 or 3 tank decommissions every day. He can help you learn all about oil tanks if you have any questions that aren’t answered by the information page.

Email Jack at [email protected] or call 503 939 9585 to learn more about oil tank decommissioning